Iron beryllium alloy



' Aug. 15, 1967 R. H. Mmmm ETAL- 3,336,170

IRON BERYLLIUM ALLOY Filed June 2,' 1965 6 Sheets-Sheet 2 l l l l I o A G//VG 77445 oo M M/ a ris l I l y I Aug. l5, 1967 R. H. `RIcHMAN ETAL IRON BERYLLIUM ALLOY Filed June 2. 1965 6 Sheets-Sheet 3 Raaf@ @/c//MA/v nvm/Ma G. any/5 INVENTORS 7' TOR/Vif@ Aug. l5, 1967 IRON BERYLLIUM ALLOY Filed June 2. 1965 EEN-E@ 6 Sheets-:Sheet 4 Wn/ma G. DAV/5 INVENTOR5 A TURA/YS R..H. RICH-MAN ETAL 3,336,170

IRON BERYLLIUM ALLOY Aug. 15, 1,967

'Filed une 2, 1965 6 Sheets-Sheet 5 Aug.`l5, 1967 R. H; RlcHMAN ETAL 3,336,170

IRON BERYLLIUM ALLOY Filed June 2, 1965 6 Sheets-Sheet 6 crau.:

INVENTORS` BY QSI-MMA A 7' GRI/Erd United States Patent 3,336,170 IRON BERYLLIUM ALLOY Roger H. Richman, Detroit, and Richard G. Davies, Taylor, Mich., assignors to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Filed June 2, 1965, Ser. No. 467,167 13 Claims. (Cl. 148-142) This application is a -continuation-in-part of our copending application, Ser. No. 267,080', led Mar. 22, 1963, now abandoned.

This invention relates to a novel class of iron-beryllium alloys and to a novel method for treating solid solutions of beryllium in iron to produce alloys having novel and useful physical characteristics.

In particular, this invention relates to supersaturated solid solutions of beryllium in iron and to novel materials produced 'hy controlled, partial thermal decomposition of the same.

More particularly, this invention relates to a method for producing novel alloys of iron and beryllium whichincludes initiating controlled thermal decomposition of supersaturated solid solutions of beryllium in iron and arresting such decomposition at a predetermined level.

It is one object of this invention to provide an ironberyllium alloy having quasi-elastic properties.

It is another object of this invention to provide `an ironberyllium alloy where the concentration of beryllium varies locally sinusoidally with distance along a given plane.

Other objects and advantages of the present invention will 4be apparent to those skilled in the art from the following description taken in conjunction with the drawings in which:

FIGURE 1 is a typical time-temperature-hardness diagram for an iron-beryllium alloy .prepared in accordance with this invention showing the change in hardness with time at several laging temperatures.

FIGURE 2 is a time-temperature-thermal decomposition diagram showing changes in the alloy structure expressed in terms of atom planes and illustrating the onset of spinodal decomposition.

FIGURE 3 is a photomicrograph of a portion of one surface of a single crystal of an alloy produced in accordance with one embodiment of this invention taken at a magnification of 75 diameters under compression with a 1.7% reduction in length.

FIGURE 4 is a photomicrograph of the same area shown in FIGURE 3 after release of the load.

FIGURE 5 is a photomicrograph of a portion of one surface of a single crystal of an alloy of similar composition to that shown in FIGURE 3 taken at a magnication of f75 diameters uner compression with an 8.4% reduction in length.

FIGURE 6 is a photomicrograph showing the same area shown in FIGURE 5 after release of the load.

FIGURE 7 is a photograph of the crystal shown in FIGURE 6 under compression providing 8.4% reduction in length at a magnification of diameters.

'FIGURE 8 is a photograph of the same area shown in FIGURE 7 after release of the load.

FIGURE 9 is a diagram showing the accumulation of residual strain with repeated cycles of plastic strain on an alloy of this invention having quasi-elastic properties.

FIGURE 10 is a photomicrograph at a magniiication of 1500 diameters of an alloy produced in the manner of the alloys shown in the preceding gures but aged at a controlled temperature for a longer period of time.

In preparing the alloys of this invention iron and beryllium are melted together in an atomic ratio suicient to provide a solution supersaturated with respect to beryllium, cast into a mold, annealed at a temperature and for a time sufficient to place all or essentially all of the beryllium into solid solution, e.g..a'bout 1l25 C., rapidly quenching the resulting solid solution to avoid atomic rearrangement incidental to gradual cooling of a supersaturated solid solution, and aging the resulting material at a predetermined controlled temperature for a predetermined time and/or to a predetermined stage of partial thermal decomposition.

The terms supersaturated and supersaturated solution as employed herein shall be understood to mean supersaturated at room temperature, e.g. 25 C.

In accordance with this invention the solid solutions employed contain at least about 20, preferably 20 to 30, atomic percent beryllium. After casting and subsequent fabrication, the work piece is heated to a temperature suflicient to allow the beryllium to become evenly distributed through the solution. Temperatures above about 1l00 C. will ordinarily be required to place beryllium in solution in the aforesaid concentrations. It is preferable to hold the temperature close to the minimum necessary for solution to prevent excessive grain growth. The heated solution is rapidly quenched in oil, water, or other suitable medium.

The quenching medium should be adapted to reduce the temperature of the solid solution at a rate sufficient to prevent any significant deg-ree of structural rearrangement normal to gradual thermal decomposition of a supersaturated solid solution. Thus, the temperature of the alloy is dropped from about 1050-1100 C. or above to maximum temperature not significantly greater than the upper temperature boundary of the subsequent controlled aging process hereinafter discussed in detail. It often will be found desirable to quench to room temperature or below. In other instances it will be lpreferred to quench to a temperature within the range between room temperature and the lower boundary of the controlled aging temperature range or to the exact temperature at which the material is to be aged in conformance with the process of this invention. It is, however, within the scope of this invention to quench rapidly to a temperature not appreciably above the aging temperature and then cool the material more slowly until the exact aging temperature is reached.

It should be understood, however, that it is within the scope of this invention to work the solid solution by any conventional technique, e..g. hot rolling, cold rolling, etc., adapted to produce 'a ne grain alloy with all of the beryllium in solid solution and that such working may be carried out either -prior to or yafter the initial quench.

After a line grained solid solution has been prepared the solution is maintained at a temperature below about 415 C., advantageously in the range of about 250 to 415 C., and preferably 290 to 380 C., until the desired degree of partial thermal decomposition is reached.

Supersaturated solid solutions of beryllium in iron thermally decompose in-an unusual manner when aged in accordance with this invention. Thus, when the supersaturated solution is rapidly quenched to entrap the relatively large beryllium content, i.e. in a manner which substantially avoids decomposition precipitation, and subsequently subjected to controlled aging at temperatures within the aforedened ranges it is found that the alloy undergoes a considerable variety of structural changes with time before precipitation of the equilibrium FeBe2 from the solid solution.

Brfiey, the structu-ral arrangements through which such alloys pass in the course of this method of thermal decomposition are as follows:

this type see International Tables for X-Ray Crystallography, N. F. M. Henry yand K. Longsdale, Eds. Kynoch Press, Birmingham, England, 1952. p. 330.

Structure 1 Massive short range order- Atomic arrangement existing after quenching and prior to controlled aging.

Structure 2 Y Pm, 3m or B2 Structure FeAl type crystal structure.

Structure 3. Fm, 3m or D03 Structure. FeAl type crystal structure.

Structure 4 Modulated structure.- Spinodal decomposition.

Structure 5.. General precipitation Structure 6 Discontinuous precipitation..-

The term partial thermal decomposition product is used herein to include Structures 2 through 5 inclusive: The term ordered structure as used herein includes and is limited to Structures 2 and 3.

BRIEF CHARACTERIZATION OF `EACH OF THE FOREGOING STRUCTURES Massive short range order Pm 3m 0r B2 structure This structure provides an ordered .arrangement of atoms occurring in a substance that started as a body centered cubic.

o-Fe or Be atom Unit Cell of Body Centered Cubic Random Solid Solution By virtue of strain energy of solute atoms -placed in a foreign lattice and complex electronic interactions incidental thereto, the solute atoms assume positions that do not require them to be nearest neighbors.

O-Fe atoms O-Fe or Be atom Unit Cell of Pm 3m or (B2) Structure of Non-Stoichiometric Composition The B2 structure in order to be perfect, is composed of 50% atom A and 50% atom B; thus, one kind of atom is at cube corners and the other kind at cube centers. In an alloy of 75% A and 25% B, viz 13e-5.7 wt. percent Be, there lare far too few Be atoms to occupy all of the center sites. Therefore, a center site may be A or B, but the corner sites are always, statistically, A.

The B2 structure in Fe-27.3 atomicpercent (5.7 wt. percent) Be alloys has a typical hardness of 425-525 DPN and `also deforms plastically by mechanical twinning. It differs from the Short Range Order structure in its plastic properties in that a small amount of elastic twinning is observed. For information on structures of Fm 3m or D03 structure This structure is a thermal decomposition progression from the B2 structure. The solute, Be, atoms tend to move as far apart as possible on the crystal lattice. Thus, in an alloy of this invention composed of 75% iron atoms and 25% beryllium atoms, the solute beryllium atoms tend to be arranged so that they 'are neither rst nor second nearest neighbors as in the following schematic lattice wherein exactly one-half of the cube centers are solute atoms in an alternating array.

Fm 3m or D03 Structure Q Fe Atoms O-Be Atoms The D03 structure in Fe-27.3 atomic percent Be alloys has a typical hardness of about 650 DPN and an existence range of about 450 to 700 DPN. Plastic deformation is by mechanical twinning but for strains of less than 20% almost all of the initial deformation is recovered by untwinning. See International Tables laforecited at page 338.

Modulaled structure The equilibrium form of Fe-Be alloys, initially supersaturated solid solutions, is a matrix of Fe-4 atomic percent Be with a second phase, FeBez, dispersed throughout. Various alloy systems reach this equilibrium stage by different routes and the Fe-Be alloys adopt the particular mechanism of a transition stage between ordering and precipitation. Since ordering implies unlike nearest neighbors, and precipitation quite the contrary, the solute atoms must first undergo some sort of clustering.'The modulated structure is clustering over distances large on an atomic scale. This may be understood 'by imagining that very thin strips of a 35 atomic percent Be alloy and a 15 atomic percent Be alloy are welded together alternately and then annealed lfor a short time to allow smoothing of the composition at the strip boundaries. The result is a composition varying sinusoidally when examined in a particular direction.

The modulated structure in F-27.3 atomic percent Be alloys has a typical hardness of about 750 DPN, an existence range of about 550 to 850 DPN, and very limited ductility.

General precipitation In this structure there is exhibited a clustering of solute atoms in definite .proportion with the solvent atoms to vform a discrete, very finely dispersed second phase. In the alloys of this invention, the second phase is FeBeg Dsconlinuous precipitation.

Occasionally, a precipitation reaction does not completely erase internal strains in a structure initially supersaturated. If these residual strains are of suiiicient magnitude, a reaction is initiated that consists of an interface or interfaces moving through each crystal, and in the portion of the grain traversed by the interface the structure is altered so that the two coexisting phases are in a lamellar array. Otherwise phrased, a discontinuous or interface controlled reaction supersedes the general precipitation throughout the matrix and causes a spatial rearrangement of phases into a lamellar structure. Usually this reaction is accompanied by very high hardness, typically above about 1000 DPN and extreme brittleness See H. K. Hardy and T. J. Heal, Report on Precipitation, Progress in Metal Physics, Interscience Publishers, Inc., N. Y. 1954, pp. 226-230.

The time at which the various structural arrangements become discernable after initiation of the controlled aging step of the instant process varies with the'temperature chosen within the defined range and the structural arrangement of the alloy at the time the treatment is initiated. It Will be understood that in transition from one structure to another the succeeding structure will appear before the Vpreceding structure disappears. Thus, for eX- ample, for an iron-beryllium alloy containing about 27.3 atomic percent beryllium which has been heated to temf peratures above about 11100 C., rapidly cooled to about 25 C. by quenching in water and subsequently reheated to initiate ycontrolled thermal decomposition, the following times and temperatures were found to bring about the results set forth inthe following table:

TABLE I.EFFECT OF TEMPERATURE ON TIME OF STRUCTURAL CHANGES IN THERMAL DECOMPOSITION OF IRON-BERYLLIUM ALLOY By using well known techniques for cold working the alloy prior to low temperature aging the -ordered structures can be induced at lower aging temperatures than are required without such treatment.

Referring now to FIGURE 1, the hardness changes shown here are indicative of structural changes occurring in the iron-beryllium alloy. Most age-hardening systems exhibit an S-shaped function of hardness vs. time at temperature. Hardness change indicating the ordering reaction lhereinbefore described is particularly evident in the curve of the Fe-Be alloy aged at 339 C.

In FIGURE 2 spinodal decomposition, the shifting of solute atoms into relatively large scale regions as opposed t-o intimate clustering indicates the advent of the modulated structure. It is known that this reaction may precede precipitation from a solid solution. The resulting solid solution is characterized by a smoothly fluctuating concentration of solute atoms when measured along any crystallographic direction. This is reflected by the very line-scale fabric-like appearance of the modulated structure prepared in accordance with lthis invention and shown in FIGURE 10.

The quasi-elastic properties of the iron-beryllium Fm 3m or D03 structure are photographically illustrated in FIGURES 3 through 7 inclusive and graphically in FIGURE 9.

For the purpose of giving those skilled in the art a better understanding of the present invention, the following examples are given by way of illustration.

EXAMPLE l A 20 pound ingot containing about 5.7 wt. percent beryllium and about 94.3 wt. percent iron Was prepared by melting the two constituents together and casting into a chill mold. Slices cut from the ingot were rolled to reduction in thickness at 1125 C. and oil quenched. The resulting band was cold rolled to 40% reduction in thickness, annealed for about 30 seconds at about 1100 -C. and water quenched.

The strips were then annealed at various temperatures and the hardness of each measured at predetermined time intervals. Annealing the quenched alloy at ,520 C. produced a classical sigmoidal hardening curve as a function of time at temperature, whereas 400 C. aging resulted in an intermediate plateau in the curve and also an ultimate hardness of about Rc 70, i.e. wherein Rc=Rockwell C-scale, or a DPN of about 1050. The effect of temperature and time on a variety of samples is illustrated in FIGURE 1. X-ray diffraction analyses of structures after various aging times revealed diffuse superlattice lines at aging times corresponding to the plateau in the hardness curve, and simultaneous splitting of the fundamental lines. It was also found by this method that strips annealed at temperatures below about 415 C. undergo the structural changes hereinbefore set forth in Table 1 before precipitation of the equilibrium FeBe2 phase from the solid solution.

EXAMPLE 2 Alloy strips prepared from the 20 pound ingot of the preceding example were hot rolled and encapsulated in quartz tubes in an atmosphere of helium. The encapsulated strips were annealed for 168 hours at 1125 C. After water quenching, single crystals in the form of rectangular parallelepipeds 0.2-0.4 inch long and 0.1-0.15 inch on a cross-sectional edge were cut from the bulk. The D03 (FeSBe) structure was produced by annealing for 2 hours at 360 C.

Slow compression of the single crystals at room ternperature were accompanied by pronounced and discrete clicking sounds. Polished surfaces on the specimens displayed coarse marking characteristic of twinning. When the load was removed, almost all evidence of deformation disappeared from the specimen surfaces. In order to make observations of the deformation mechanism, a clamping device is employed to maintain load on the specimen during metallographic and Xray examination. FIGURE 3 sh-ows a surface relief on a single crystal polished and then compressed to provide a 1.7% reducti-on in length. FIGURE 4 shows the area shown in FIG- URE 3 after removal of the load. In FIGUREl 5 there is shown a surface of a similar crystal compressed to provide an 8.4% reduction in length. In FIGURE 6 there is shown the same surface shown in FIGURE 5 after the l-oad has been removed. The outer configuration of this crystal under compression andafter release is shown in FIGURES 7 and 8 respectively.

X-ray diffraction coupled with trace analyses of the surface markings indicated that the deformation and reformation results from mechanical twinning rather than phase transition.

The compression and release of similar crysals indicated that the amount of unrecoverable plastic strain is a function of the total strain. Thus, for 3% plastic strain, the residual strain for a single compression and release of a virgin crystal was too small to be evaluated, i.e. the change was within the range of experimental error for conventional instruments adapted for use in making measurements of this type. A virgin crystal of the same initial orientation retained 0.25% strain after a single plastic strain. Continued c-ompression-unload cycles each of about 10% plastic strain were effected and the accumulation of residual strain measured. The load-contraction curve defined by six such cycles is shown in FIGURE 9 of the drawings.

EXAMPLE 3 Polycrystalline strips prepared in accordance with the preceding examples including hot rolling and oil quenching were annealed at 360 C. for two hours to produce the Fe3Be (D03) structure. Tensile specimens with a reduced gauge section of 0.050 x 0.050 x 1" were machined from the strip. In this group of specimens failure occurred at about 220,000 p.s.i.

In another test a tensile specimen as above described was annealed for four days at 1125 C. prior to low temperature aging for two hours at 360 C. A bambootype grain structure was observed and this specimen sustained more than plastic strain before necking locally to failure. Other specimens prepared in like manner were tested in compression. Strain hardening was extremely rapid and the onset of plastic flow was difficult to detect. Two such specimens of identical composition were compressed in several cycles of load-unload. The results in terms of yield stress, nal stress, plastic strain, and residual strain per cycle are `summarized in the following table. The final stress values set forth in this table are calculated from actual specimen dimensions at the corresponding strain.

TABLE II.-COMPRESSION TESTS OF POLYCRYSTALLINE FEI-5.7 Bo HOT BAND, ANNEALED 2 HOURS AT 360 C.

It will be understood by those skilled in the art that different working methods and conditions for preparing the alloy will bring about modifications in degree in the physical properties of the alloys of this invention.

EXAMPLE 4 An alloy strip was prepared in accordance with Example 2 except that aging was continued at 323 C. until spinodal decomposition replaced the D03 (FeaBe) structure as the primary structural arrangement of the alloy. Aging was terminated after 4000 minutes. In FIGURE 10 there is shown at a magnification of 15100` diameters the surface relief on a polished single crystal thus prepared.

The modulated structure, as are all the partial decomposition products, is a consequence of heat treatment. Consequently it can be induced in single or polycrystals Its hardness is reflected by very high strength and limited ductility. For example, typical specimens showed the following mechanical properties:

An alloy was prepared as in Example 2 using an aging temperature of 360 C. and an aging time of 120 minutes to produce the D03 structure, DPN `about 600. This was corroborated by the following measurements using X-ray diffraction analysis (single crystal monochromator).

Actual 2 t1, Identification (Miller Planar Spac- Theoretical Degrees Indices) ing, A. Based on 220 Fundamental lll-Superlattice 3. 213 3. 230 20o-superlattice 2. 707 2. 797 220-Fundarnental 1. 978 l. 978

The value of alloys prepared in accordance with this method in structural or other applications resides in the fact that the alloy can be fabricatedand the final properties then accomplished by heat treatment after forming.

The term cooling the solid solution at a rate sufficient to avoid significant thermal decomposition as used herein means that the alloy, heated to a temperature sufficient to place the beryllium constituent into solid solution with the iron constituent, is quenched at a sufficiently rapid rate to cause essentially all of the solute constituent, beryllium, to remain in the iron in the form of a supersaturated solid solution. A determination as to whether or not the quench was sufficiently rapid to achieve the desired result can be made by measuring the hardness of the resultant solid or checking its structure by X-ray diffraction or transmission electron microscopy. Hardness is indicative of the degree of thermal decomposition as hereinbefore pointed out. If such hardness is in excess of that characterizing the partial thermal decomposition state desired, it is obvious that this state cannot be obtained from further aging. In such case the alloy could be heated to the temperature above that required to place all of the beryllium into solid solution and this step followed by a more rapid quenching. To one skilled in the art this will present no particular problem, since this step may be carried out, as hereinbefore recited, by conventional oil or water quenching techniques.

The time required to bring about the desired stage of partial thermal decomposition or atomic rearrangement is predictable and measurable with a minimum of routine testing. This time, as hereinbefore pointed out, varies with the .aging temperature and the structural arrangement of the alloy at the time the aging is initiated. The latter can be determined by aging for various times and testing via X-ray diffraction or transmission electron microscopy etc. For instance, the D03 structure is identified by detection and measurement of two superlattice reections at angles below the first fundamental reection whereas only one such superlattice reflection identities the B2 structure. Areas of greater and lesser beryllium concentration are determinable by X-ray diffraction. Incipient precipitation is determinable by transmission electron microscopy. A guide as to time at 4 separate aging temperatures is set forth hereinbefore in Table I.

Although the invention has been described with a certain degree of particularity, it is understood that the present invention disclosure has been made only by way of example, and that changes in the details of the process may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. A solution heat treated-aged alloy of iron and beryllium having a Diamond Pyramid Number above about 450 and below about 700, a beryllium concentration of about 20 to about 30 atomic percent, remainder consisting essentially of iron, and a D03 type crystallographic structure.

2. A solution heat treated-aged alloy of iron and beryllium having a Diamond Pyramid Number in the range of about 550 to about 850 and a beryllium concentration of about 20 to about 30 atomic percent, remainder consisting essentially of iron, wherein the beryllium atoms are distributed throughout said'alloy in regularly repeated areas of greater and lesser concentration.

3. A solution heat treated-aged alloy of iron and beryllium having a Diamond Pyramid Number in the range of about 550 to about 850 and a beryllium concentration of about 20 to about 30 atomic percent, remainder consisting essentially of iron, wherein the concentration of beryllium atoms varies sinusoidally with distance along a given plane.

4. The method of producing van alloy which comprises heating iron and beryllium until a solution of beryllium in iron is formed having a beryllium concentration in the range of about 20v toabout 30 atomic percent, cooling said solution at a rate sufficient to yield a solid solution having a Diamond Pyramid Number at least 50 below 850, heat treating the resulting solid solution at a temperature suficient to effect partial thermal decomposition of said solid solution and below about 415 C. for `a time sufficient to effect significant thermal decomposition. of said solid solution as evidenced by an increase in hardness of said solid solution by a Diamond Pyramid Number increase of at least about 50, and terminating said heat treatment while the Diamond Pyramid Number of said solid solution is below about 850.

5. The method of producing an alloy which comprises heating iron and beryllium until a solution of beryllium in iron is formed having a beryllium concentration in the range of about 20 to vabout 30 atomic percent, cooling said solution at a rate sufficient to avoid significant thermal decomposition thereof and to yield a solid solution having a Diamond Pyramid Number of below about 800, heat treating the resulting solid solution at a temperature suflicient to effect partial thermal decomposition of said solid solution and below about 415 C. for a time suflcient to effect significant thermal decomposition of said solid solution as evidenced by an increase in hardness of said solid solution by a Diamond Pyramid Number increase of above about 50, and terminating said heat treating while the beryllium of said solid solution is distributed therein in a manner such that the concentration of beryllium atoms in said solid solution varies locally sinusoidally with distance along a given plane and while the Diamond Pyramid Number of said solid solution is below about 850.

6. The method of producing an alloy which comprises heating iron and beryllium until a solution of beryllium in iron is formed having a beryllium concentration in the range of about 20 to about 30 atomic percent, cooling said solution at a rate sufficient to avoid significant thermal decomposition thereof and to yield a solid solution having a Diamond Pyramid Number of below about 600, heat treating the resulting solid solution at a temperature in the range of about 250 C. to about 415 C. for a time sufficient to effect significant partial thermal decomposition of said solid solution as evidenced by an increase in hardness of said solid solution by a Diamond Pyramid Number increase of above about 50, and terminating said heat treating before significant amounts of said beryllium precipitate from said solid solution and while the Diamond Pyramid Number of said solid solution is below about 700.

7. The method of producing an alloy which comprises heating iron and beryllium until a solution of beryllium in iron is formed having a beryllium concentration in the range of -about 20 to about 30 atomic percent, cooling said solution at a rate sufficient to yield a solid solution having a Diamond Pyramid Number of below about 600, heat treating the resulting solid solution at a temperature sufficient to effect partial thermal decomposition of said solid solution and below about 415 C. for a time sufficient to effect significant thermal decomposition of said solid solution as evidenced by an increase in hardness of said solid solution by a Diamond Pyramid Number increase of above about 50, and terminating said heat treatment while the Diamond Pyramid Numberl of said solid solution is below about 850.

8. The method of producing an alloy which comprises heating iron and beryllium until a solution of beryllium in iron is formed having a beryllium concentration in the range of about 20 to about 30 atomic percent, cooling said solution at a rate sufficient to yield a solid solution having a Diamond Pyramid Number of below about S50, heat treating the resulting solid solution at a temperature sufficient to effect partial thermal decomposition of said solid solution and below about 415 C. for a time sufficient to effect significant thermal decomposition of said solid solution as evidenced by an increase in hardness of said solid solution by a Diamond Pyramid Number increase of above about 50, and terminating said heat treatment while the Diamond Pyramid Number of said solid solution is below about 850.

9. The method of producing an alloy which comprises heating iron and beryllium until a solution of beryllium in iron is formed having a beryllium concentration in the range of about 20 to about 30 atomic percent, cooling said solution at a rate sufficient to yield a solid solution having a Diamond Pyramid Number of below about 450', heat treating the resulting solid solution at a temperature sufficient to effect partial thermal decomposition of said solid solution and below about 415 C. for a time sufficient to effect significant thermal decomposition of said solid solution as evidenced by an increase in hardness of said solid solution by a Diamond Pyramid Number increase of above about 50, and terminating said heat treatment while the Diamond Pyramid Number of said solid solution is below about 850.

10. The method of producing an alloy which comprises heating iron and beryllium until a solution of beryllium in iron is formed having a beryllium concentration in the range of about 20 to about 30 atomic percent, cooling said solution at a rate sufficient to avoid significant thermal decomposition thereof and to yield a solid solution having a Diamond Pyramid Number of below about 600, heat treating the resulting solid solution at a temperature in the range of about 250 C. to about 415 C. for a time sucient to effect significant partial thermal decomposition of said solid solution as evidenced by an increase in hardness of said solid solution by a Diamond Pyramid Number increase of above about 50, and terminating said heat treating before significant amounts of said beryllium precipiate from said solid solution and while the Diamond Pyramid Number of said solid solution is below about 850.

11. The method of producing an alloy which comprises heating iron and beryllium until a solution of beryllium in iron is formed having a beryllium concentration in the range of about 20 to about 30 atomic percent, cooling said solution at a rate sufficient to avoid significant thermal decomposition thereof and to yield a solid solution having a Diamond Pyramid Number of below about 600, heat treating the resulting solid solution at a temperature in the range of about 290 C. to about 380 C. for a time sufficient to effect significant partial thermal decomposition of said solid solution as evidenced by an increase in hardness of said solid solution by a Diamond Pyramid Number increase of above about 50, and terminating said heat treating before signicant amounts of said beryllium precipitate from said solid solution and while the Diamond Pyramid Number of said solid solution is below about 700. f

12. The method of producing an alloy which comprises heating iron and beryllium until a solution of beryllium in iron is formed having a beryllium concentration in the range of about 20 to about 30 atomic percent, cooling said solution at a rate sufficient to avoid significant thermal decomposition thereof and to yield a solid solution having a Diamond Pyramid Number of below about 600, heat treating the resulting solid solution at a temperature suffcient to effect partial thermal decomposition of said solid solution and below about 415 C. for a time sufficient to effect significant partial thermal decomposition of said solid solution as evidenced by an increase in hardness of said solid solution by a Diamond Pyramid Number increase of above about 50, and terminating said heat treating while the beryllium content of said solid solution is distributed throughout said solid solution in a pattern of 1 1 substantial regularity and while the Diamond Pyramid Number of said solid solution is below about 700.

13. The method of producing an alloy which comprises heating iron and beryllium until a solution of beryllium in iron is formed having a beryllium concentration in the range of about 20 to about 30 atomic percent, cooling said solution at a rate sufficient to avoid significant thermal decomposition thereof and to yield a solid solution having a Diamond Pyramid Number of below about 600, heat treating the resulting solid.solution at a temperature suicient to effect partial thermal decomposition of said solid solution and below about 415 C. for a time suicient to effect signicant partial thermal decomposition of said solid solution as evidenced by an increase in hardness of References Cited UNITED STATES PATENTS 4/1933 Dean 75--123 OTHER REFERENCES The Beryllium-Iron System, R. I. Teitel et al., Journal of Metals, vol. 1, pp. 285-296.

said solid solution by a Diamond Pyramid Number in- 15 DAVID L. RECK, Primary Examiner. 

1. A SOLUTION HEAT TREATED-AGED ALLOY OF IRON AND BERYLLIUM HAVING A DIAMOND PYRAMID NUMBER ABOVE ABOUT 450 AND BELOW ABOUT 70, A BERYLLIUM CONCENTRATION OF ABOUT 20 TO ABOUT 30 ATOMIC PERCENT, REMAINDER CONSISTING ESSENTIALLY OF IRON, AND A DO3 TYPE CRYSTALLOGRAPHIC STRUCTURE. 